igneous
Basalt
Mafic Igneous Rock
Hardness (Mohs scale): 6; Color: Dark grey to greenish-black; Luster: Dull or sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Color
- Dark grey to greenish-black
- Luster
- Dull or sub-metallic
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Physical properties
Hardness (Mohs scale): 6; Color: Dark grey to greenish-black; Luster: Dull or sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic islands.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for stone carving and as an industrial fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon (the lunar maria) and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals. It is ubiquitous in volcanic regions and ocean floor outcroppings.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
Igneous
Magnetite
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Magnetite
Magnetite (Fe3O4)
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